It is well known that a reduced amount of diurnal activity and depressive symptoms may be noted in elderly people. There is a report that the amount of diurnal activity is closely related to sleep, and sleep disorders may often reduce the amount of diurnal activity, and the amount of diurnal activity correlates with the quality and the quantity of sleep at night [Psychiatry Clin Neurosci Vol. 54, 309-310 (2000)]. The incidence of sleep disorders markedly increases with aging. In the background of the increased incidence of sleep disorders in the elderly people, there are often age-related changes in sleep as represented by increased cases of arousal during sleep, difficulty in resuming sleep after arousal, curtailment in total sleeping hours, reduced sleep efficiency, and reduced slow wave sleep. Overlapping these physiological changes, it is believed, a great variety of sleep-interrupting factors may occur which results in the onset of sleep disorders of the elderly [Medical Frontier (Saisin Igaku) Vol. 59, 468-475 (2004)].
On the other hand, a variety of mental disorders are believed to induce the reduced amount of diurnal activity and/or depressive symptoms directly or via symptoms such as sleep disorders. For example, in patients with schizophrenia, there are known not only insomnia resulting from difficulty in sleeping and from arousal during sleep but also sleep disorders resulting from disturbances in the sleep and the waking rhythm such as changes in life patters and irregular daily lives. Among mental disorders, emotional disturbance is frequently accompanied by sleep disorders and depressive symptoms: unipolar depression exhibits insomniac symptoms such as difficulty in sleeping, arousal during sleep, early morning arousal, lack of sensation of deep sleep, and curtailment of sleeping hours, and the bipolar depression exhibits insomniac symptoms similar to those in the unipolar depression, but in the bipolar depression unlike the unipolar depression, hypersomnia such as repeated napping is often noted. In addition, neurological disorders also cause sleep disorders and depressive symptoms, and as neurological disorders that are often accompanied by sleep disorders, there can be mentioned cerebral degenerative disorders, dementia, Parkinson's disease, lethal familial insomnia, sleep-related epilepsy, epileptic seizure wave state during sleep, sleep-related headache and the like [Supplement, Nippon Rinsho (Japanese Journal of Clinical Medicine) Vol. 39, 231-248 (2003)].
In recent years, methods of using an actigraph are attracting attention as methods of evaluating the quality of sleep and the amount of activity. The actigraph is a wristwatch-type device that has built in a sensor for measuring the amount of activity and is worn on the nondominant arm to measure the amount of activity night and day with one week as a unit thereby to assess changes in the amount of activity. Analyzing the result of this actigraph measurement, by computer software, is believed, to be very useful for diagnosing, observing the progress of, and judging the therapeutic effects of sleep disorders, the reduced amount of activity etc. associated with mental diseases, neurological diseases and aging.
As therapeutic methods for the reduced amount of diurnal activity and depressive symptoms due to such sleep disorders and reduced mental and physical functions, there are psychotherapeutic approaches, non-drug therapies, and drug therapies. Non-drug therapies include high illumination radiation, which is now aggressively used in the treatment of seasonal emotional disturbance and circadian rhythm sleep disorders. Though vitamin B12 and benzodiazepine hypnotics etc. are being used as drug therapies for the treatment of sleep disorders and depressive symptoms, none of them can be said to be very effective, and the establishment of drug therapies is being awaited. For the treatment of emotional disturbance and neurological diseases, it is common to combine antidepressants and psychotropic drugs with hypnotics. However, there are currently no safe and effective compounds that have therapeutic effects for the treatment of the reduced amount of diurnal activity and depressive symptoms due to sleep disorders and reduced mental and physical functions.
As a compound that controls sleep and behavior, cannabinoids are known. Cannabinoids are reported to affect memory and learning [Nature Vol. 388, 773-778 (1997)] and eating, relaxation and sleep [J Neurosci Vol. 21, 5344-5350 (2001)] via cannabinoid receptors in the brain. As endogenous cannabinoids in the human body, arachidonic acid-containing compounds, such as anandamide and 2-arachidonoyl monoglycerol, are known. These cannabinoids, even when orally ingested, undergo hydrolysis and thus are not absorbed as they are. Reports on them so far only describe in vitro experiments or experiments on the administration of receptor inhibitors.
Thus, it was not clear at all whether compounds containing arachidonic acid as a constituent fatty acid ingested by humans affect the reduced amount of diurnal activity and depressive symptoms.    Non-patent document 1: Psychiatry Clin Neurosci Vol. 54, 309-310 (2000)    Non-patent document 2: Medical Frontier (Saisin Igaku) Vol. 59, 468-475 (2004)    Non-patent document 3: Supplement, Nippon Rinsho (Japanese Journal of Clinical Medicine) Vol. 39, 231-248 (2003)    Non-patent document 4: Nature Vol. 388, 773-778 (1997)    Non-patent document 5: J Neurosci Vol. 21, 5344-5350 (2001)